Gel-coated seed

ABSTRACT

A gel-coated seed is provided, which has sufficient strength for handling just after the production thereof and after the recovery following the storage under drying, and has a good property in terms of standing-up of seedling. The gel-coated seed includes: a seed of a plant; a coating gel-layer, which coats the seed, consisting of alginic acid-based aqueous gel gelled in the presence of a multivalent metal ion; and grains consisting of water-containing hydrophilic polymer, which is resistant to the multivalent metal ion, distributed in the coating gel-layer.

BACKGROUND OF THE INVENTION

[0001] (1) Field of the Invention

[0002] The present invention relates to a gel-coated seed.

[0003] (2) Description of the Related Art

[0004] The gel-coated seed technology (i.e., technology of coating seedswith gel) improves a conventional labor-intensive agriculture includingexcessive sowing in the field taking low gemmation rate of seeds intoconsideration, that is, taking the fact that the bud barely or hardlycomes out from the coating gel-layer after the gel-coated seedgerminates, and thinning out after gemmation.

[0005] The technology is an epoch-making technology, by which a seedlingcan securely be obtained from a grain of seed with the aid of water orother constituent contained in a coating gel-layer and furthermore acrop can be obtained. The technology enables the use of F1 seeds, whichis excellent and very expensive, thereby attaining significantimprovement in yield and quality. The technology is really good news forJapanese agriculture, which should survive in the condition that highquality and cheap vegetables and flowers are imported from neighboringAsian countries.

[0006] At the beginning, the coating gel-layer of the-gel-coated seedwas composed of only alginic acid-based aqueous gel. However, since thealginic acid-based aqueous gel is relatively hard, such a gel-coatedseed had a problem in terms of “standing-up of seedling” (explainedbelow). In other words, since the alginic acid-based aqueous gel isrelatively hard, the bud of a coated plant may become difficult to growor may not come out from the coating gel-layer to die. Consequently,such a measure has been employed that grains consisting of hydrophilicpolymer and water are distributed in the coating gel-layer.

[0007] In this specification, the “standing-up of seedling” is definedas a condition that a gel-coated seed sown in a field germinates, thebud comes out from the coating gel-layer and further comes out from thesoil of the field, and it becomes a defect-free plant body with thefirst leaf thereof being completely out (i.e., being completelyextends). A ratio (%) of seeds, each of which has a good property interms of “standing-up of seedling” described above, relatively to allseeds sown is called “ratio of standing-up of seedling” in thisspecification.

[0008] The gel-coated seed, in which grains consisting ofwater-containing hydrophilic polymer are distributed in the coatinggel-layer consisting of alginic acid-based aqueous gel, is produced, forexample, by the following manner.

[0009] A weighing is carried out so that the concentration of sodiumalginate becomes 0.9 wt % and the final concentration of powdered starchpolyacrylate-based hydrophilic polymer (i.e., starch-acrylic acid graftpolymer) becomes 0.2 wt %, then water is added thereto so as to dissolvethe sodium alginate sufficiently. At that time, the hydrophilic polymerabsorbs water to be granular and is dispersed by stirring. By using thisliquid dispersion (i.e., gel-forming liquid in which the grainsconsisting of the water-containing hydrophilic polymer are dispersed), adroplet thereof is formed at a lower end of a hollow tube, into which aseed is introduced from the interior of the hollow tube, and then theresultant droplet is dropped in a solution containing multivalent metalion having concentration of 12-14 wt % such as an aqueous solution(hardening liquid) of calcium chloride, thereby obtaining a gel-coatedseed including a coating gel-layer, which is insolubilized againstwater.

[0010] Since the strength of thus produced coating gel-layer is verystrong, in order to attain a better property in terms of standing-up ofseedling, a gel-coated seed having low concentration of alginate hasbeen produced, by which a three-dimensional network structureobstructing the growth of the seed due to the alginic acid in thecoating gel-layer is weakened.

[0011] In such a case, however, since the strength of the coatinggel-layer is deteriorated, when a hopper is used upon handling of thegel-coated seeds such as mechanical sowing, the gel-coated seed iscrushed and deformed causing the hopper stuck and otherwise the surfacelayer of the gel-coated seed comes off causing the mechanical sowingunable to be carried out, that is, handling property thereof isdeteriorated and the originally intended effect for the gel-coated seedcannot be attained.

[0012] Therefore, in order to attain sufficient strength of the coatinggel-layer in such a condition that the using amount of the alginate isreduced, the amount of the hydrophilic polymer is significantlyincreased.

[0013] By this measure, the coating gel-layer having sufficient strengthin usual use is obtained. However, when the coating gel-layer is driedfor the purpose of storing the gel-coated seed and thereafter thecoating gel-layer is provided with water for sowing the gel-coated seed,the coating gel-layer is not sufficiently recovered, that is, thecoating gel-layer becomes spongy deteriorating its strengthsignificantly and the gel-coated seed thus obtained becomes hard to behandled.

SUMMARY OF THE INVENTION

[0014] It is therefore an objective of the present invention to solvethe above problem and to provide a gel-coated seed, which has sufficientstrength for handling just after the production thereof and after therecovery following the storage under drying, and has a good property interms of standing-up of seedling.

[0015] The inventor has carried out investigation on a starchpolyacrylate-based hydrophilic polymer conventionally employed forattaining the objective described above. As a result, the inventor hasfound that when a hydrophilic polymer once contained water is dried andrecovered by absorbing water, the hydrophilic polymer coming in contactwith a multivalent metal ion (i.e., gelling agent) hardly absorbs waterand hardly recovers, that is, upon absorbing water and recovering of thecoating gel-layer of the gel-coated seed, only the three-dimensionalnetwork structure portion due to the alginic acid is recovered causingthe coating gel-layer to be spongy, therefore the strength necessary forthe coating gel-layer cannot be obtained.

[0016] In order to attain the above objective, the present invention isto provide a gel-coated seed comprising: a seed of a plant; a coatinggel-layer, which coats the seed, consisting of alginic acid-basedaqueous gel gelled in the presence of a multivalent metal ion; andgrains consisting of water-containing hydrophilic polymer, which isresistant to the multivalent metal ion, distributed in the coatinggel-layer.

[0017] With the construction described above, the gel-coated seed of thepresent invention significantly well recovers upon absorbing water afterthe storage under drying in comparison with a conventional gel-coatedseed proposed in, for example, Japanese Patent Application Laid-Open No.H5-56707, even when the amount of the hydrophilic polymer is increased.Moreover, just after the production thereof and after the recoveryfollowing the storage under drying, the gel-coated seed of the presentinvention has sufficient strength for handling and a good property interms of standing-up of seedling.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] In the present invention, the multivalent metal ion, which formsthe alginic acid-based aqueous gel, is a metal ion having a valenceequal to or higher than two and is not a heavy metal ion. Themultivalent metal ion is, for example, calcium ion, aluminum ion, andiron ion.

[0019] In the present invention, the hydrophilic polymer that isresistant to the multivalent metal ion means such a hydrophilic polymerthat if the multivalent metal ion is, for example, a calcium ion, ahydrophilic polymer grain, which absorbs water in a sodium alginateaqueous solution of 0.9 wt % concentration so as to be granular, isimmersed in a calcium chloride aqueous solution of 20 wt % concentrationand taken out therefrom by filtration after one minute, wherein theweight change of the hydrophilic polymer is not more than 10%. Here, theweight change means a change in weight of the hydrophilic polymer, whichis expressed by an absolute value, before and after the contact of thehydrophilic polymer with the calcium chloride aqueous solution.

[0020] If the weight change of the hydrophilic polymer is more than 10%,the recovery property of the gel-coated seed after the storage underdrying is deteriorated and therefore, the effect of the presentinvention cannot be attained.

[0021] The hydrophilic polymer that is resistant to the multivalentmetal ion is, for example, a sulfonic-based hydrophilic polymer,nonionic-based hydrophilic polymer, and carboxymethylcellulose-basedhydrophilic polymer. Especially, a carboxymethylcellulose-basedhydrophilic polymer is preferable since it is not toxic and isbiodegradable, causing no problem in terms of the pollution of theenvironment.

[0022] Other than these hydrophilic polymers described above, forexample, as for a starch polyacrylate-based hydrophilic polymer,hydrophilic groups in the polymer crosslink with each other by a calciumion and therefore, the polymer shrinks and cannot absorb water again.

[0023] The calcium ion-resistant hydrophilic polymer is normally addedthereto so that the concentration thereof becomes equal to 0.2 wt %.However, in order to attain a better property in terms of standing-up ofseedling, the concentration thereof is preferably 0.5-0.8 wt %. As forthe gel-coated seed of the present invention, even when the using amountof the hydrophilic polymer is increased as in the latter case, thegel-coated seed has high strength and excellent handling property justafter the formation of the coating gel-layer, and such high strength andexcellent handling property can be completely recovered by absorbingwater after the storage under drying.

[0024] Further, when the using amount of the calcium ion-resistanthydrophilic polymer is set to be 0.5-0.8 wt %, tolerance of theconcentration of the calcium chloride aqueous solution as the hardeningliquid extends.

[0025] So far, strict control has been necessary for the concentrationof the calcium chloride aqueous solution, which has been used forproducing a conventional gel-coated seed (including a gel-coated seed,in which grains consisting of water-containing hydrophilic polymer aredistributed in a coating gel-layer consisting of alginic acid-basedaqueous gel).

[0026] That is, if the concentration of the calcium chloride aqueoussolution is lower than 12 wt %, the strength of the gel-coated layerbecomes too weak to handle, causing a problem that the mechanical sowingcannot be carried out. On the other hand, if the concentration of thecalcium chloride aqueous solution is higher than 14 wt %, the gel-coatedseed cannot recover sufficiently, and the bud hardly comes out from thecoating gel-layer after the gel-coated seed germinates. This has been areason why the concentration of the calcium chloride aqueous solutionmust be controlled in the narrow range of 12-14 wt %. This concentrationgradually decreases as the manufacturing number of the gel-coated seedincreases. Further, this concentration changes depending upon thevaporization of water. Thus, since the range of the concentration to beusable is very narrow, the concentration has to be controlled strictlyeven if the concentration is controlled by the density of the solution.

[0027] However, if the using amount of the calcium ion-resistanthydrophilic polymer is set to be 0.5-0.8 wt % upon formation of theaqueous gel-forming solution, the coating gel-layer having suitablehardness can be obtained when the concentration of the calcium chlorideaqueous solution as the hardening liquid is 10-20 wt %. Thus, the usableconcentration range of the calcium chloride aqueous solution becomeswider, especially at the high concentration side, as a result, thecontrol of the concentration becomes easy to be carried out, therebymaking the quality control easier.

[0028] The concentration of sodium alginate is set to be 0.9-1.3 wt % inthe gel-forming solution, in which the grains consisting ofwater-containing hydrophilic polymer are dispersed.

[0029] When the using amount of the calcium ion-resistant hydrophilicpolymer is set to be 0.5-0.8 wt %, the concentration of sodium alginatecan be reduced to be 0.5-0.6 wt % in the gel-forming solution, by whichthe gel-coated seed to be obtained has an excellent property in terms ofstanding-up of seedling, and excellent strength and handling propertyjust after the formation of the coating gel-layer and after the recoveryby absorbing water following the storage under drying.

[0030] The gel-coated seed of the present invention can be produced in asimilar manner to that of a conventional gel-coated seed except for apoint that the kind of the hydrophilic polymer is different from that ofthe conventional gel-coated seed.

[0031] The gel-coated seed thus prepared can be stored by drying themfor a long period of time so that they can be sown in a necessary placeat a necessary time.

[0032] The drying is carried out at relatively low temperature,preferably at ordinary temperature, so that the seed is not damaged.However, if the drying takes a long period of time, the seed in thegel-coated seed may undesirably germinate. Therefore, the period of timefor drying is preferably shortened by using ventilation. The gel-coatedseed thus dried is stored at ordinary temperature or under cooling.

[0033] The coating gel-layer is recovered by immersing the gel-coatedseed in water or by the other methods before sowing. It usually takes3-16 hours to be recovered depending upon temperature and the thicknessof the coating gel-layer.

[0034] In the recovery, the diameter of the gel-coated seed principallybecomes uniform and the shape thereof recovers its spherical shape. Ifthe recovered gel-coated seed is spherical having a diameter of 70-170relatively to a diameter of 100 for the gel-coated seed before dryingand the uniformity of the diameter among the gel-coated seeds is good,the gel-coated seed can be mechanically sown by replacing a grating of asowing machine. In general, if the recovered gel-coated seed is toosmall in diameter, the bud cannot come out from the coating gel-layerbecause the gel-coated layer is hard, on the other hand, if thegel-coated seed is too large in diameter, the gel-coated seed is softand does not have necessary strength, therefore they cannot be handledwith a hopper.

EXAMPLES

[0035] In the following, the gel-coated seed of the present inventionwill be explained in detail with examples and comparative examples.

Comparative Example 1

[0036] Sodium alginate and powdered starch polyacrylate-basedhydrophilic polymer (hereinafter, polymer A) were weighed so that eachconcentration in a solution became 0.9 wt % and 0.2 wt %, respectivelyand stirred well with adding water. The water-containing hydrophilicpolymer grain dispersed in a gel-forming solution was observed with amicroscope revealing that the diameter of the grain was 0.1-0.2 mm andthe average diameter was 0.15 mm.

[0037] By using this dispersion solution, its droplet was formed at alower end of a hollow tube, then a seed of a long onion was introducedinto the droplet from the interior of the hollow tube and then, thedroplet was dropped in calcium chloride aqueous solutions (hardeningliquids) having the calcium chloride concentrations of 10, 12, 14, and16 wt %, thereby preparing gel-coated seeds (189 seeds per eachsolution), in which grains consisting of water-containing hydrophilicpolymer were distributed in a coating gel-layer consisting of alginicacid-based aqueous gel. The prepared gel-coated seed was approximatelyspherical having a diameter of about 1 cm (hereinafter, the same).

[0038] As for the gel-coated seed, which was prepared by using thehardening liquid of 10 wt % calcium chloride concentration, apparentlyhad a soft coating gel-layer and could not be handled with a hopper. Onthe other hand, as for the gel-coated seed, which was prepared by usingthe hardening liquid of 16 wt % calcium chloride concentration, thecoating gel-layer was too hard, therefore it was considered that the budcould not come out from the coating gel-layer.

[0039] Consequently, as for the gel-coated seeds, which were prepared byusing the hardening liquids of 10 and 16 wt % calcium chlorideconcentration, the further investigation was not carried out.

[0040] The gel-coated seeds, which were prepared by using the hardeningliquids of 12 and 14 wt % calcium chloride concentration, were oncedried with ventilation and thereafter immersed in water at roomtemperature for 7 hours so as to recover the coating gel-layer.

[0041] At this time, each recovered gel-coated seed was spherical havingweight of 120-148 relatively to weight of 100 for the gel-coated seedbefore drying and the uniformity among the gel-coated seeds wasexcellent. The recovered gel-coated seed was free from peeling of itssurface and crack, and the diameter thereof was increased by only about10% at most. (Hereinafter, the recovery of the level as described aboveis defined as “satisfactory”.)

[0042] Further, the rupture stress (breaking stress) was measured andthe result revealed that the recovered gel-coated seed was suitable tohandling with a hopper and it appeared that the bud could come out fromthe coating gel-layer. Consequently, the ratio of standing-up ofseedling was investigated.

Comparative Example 2

[0043] In order to improve the ratio of standing-up of seedling, theamount of the polymer A was increased compared with ComparativeExample 1. That is, sodium alginate and the polymer A were weighed sothat each concentration in a solution became 0.9 wt % and 0.8 wt %,respectively and stirred well with adding water. The water-containinghydrophilic polymer grain dispersed in a gel-forming solution wasobserved with a microscope revealing that the diameter of the grain was0.1-0.2 mm and the average diameter was 0.15 mm.

[0044] Similarly to Comparative Example 1, by using this dispersionsolution, its droplet was formed at a lower end of a hollow tube, then aseed of a long onion was introduced into the droplet from the interiorof the hollow tube and then, the droplet was dropped in calcium chlorideaqueous solutions (hardening liquids) having the calcium chlorideconcentrations of 10, 12, 14, and 16 wt %, thereby preparing gel-coatedseeds (189 seeds per each solution), in which grains consisting ofwater-containing hydrophilic polymer were distributed in a coatinggel-layer consisting of alginic acid-based aqueous gel.

[0045] Similarly to Comparative Example 1, the gel-coated seeds, whichwere prepared by using the hardening liquid of 10 and 16 wt % calciumchloride concentration, apparently were not suitable for use, thereforethe further investigation was not carried out as to these gel-coatedseeds.

[0046] The gel-coated seeds, which were prepared by using the hardeningliquids of 12 and 14 wt % calcium chloride concentration, were oncedried with ventilation and thereafter immersed in water at roomtemperature for 7 hours so as to recover the coating gel-layer.

[0047] However, the recovered coating gel-layer was spongy and thereforethe gel-coated seed did not have strength large enough to be handledwith a hopper or to be sown by using an automatic sowing machine.Consequently, the further investigation was not carried out as to thesegel-coated seeds.

Example 1

[0048] An investigation was carried out using the same procedure as inComparative Example 1 except for a point that a powderedcarboxymethylcellulose-based hydrophilic polymer (hereinafter, polymerB) was employed instead of the polymer A. That is, sodium alginate andpolymer B were weighed so that each concentration in a solution became0.9 wt % and 0.2 wt %, respectively and stirred well with adding water.The water-containing hydrophilic polymer grain dispersed in agel-forming solution was observed with a microscope revealing that thediameter of the grain was 0.1-0.2 mm and the average diameter was 0.15mm.

[0049] The grain of the hydrophilic polymer B, which absorbed water in asodium alginate aqueous solution of 0.9 wt % concentration so as to begranular, was immersed in a calcium chloride aqueous solution of 20 wt %concentration and taken out therefrom by filtration after one minute,then the weight change of the hydrophilic polymer was measured. Theweight decreased by 5%.

[0050] By using this dispersion solution, its droplet was formed at alower end of a hollow tube, then a seed of a long onion was introducedinto the droplet from the interior of the hollow tube and then, thedroplet was dropped in calcium chloride aqueous solutions (hardeningliquids) having the calcium chloride concentrations of 10, 12, 14, and16 wt %, thereby preparing gel-coated seeds (189 seeds per eachsolution), in which grains consisting of water-containing hydrophilicpolymer were distributed in a coating gel-layer consisting of alginicacid-based aqueous gel.

[0051] As for each gel-coated seed thus prepared, the coating gel-layerhad strength large enough to be handled and it appeared that the budcould come out from the coating gel-layer. Therefore, additionalgel-coated seeds (112 seeds per each solution) were prepared similarly,in which the calcium chloride concentration was 8 and 20 wt %. As aresult, the gel-coated seed of the calcium chloride concentration of 8wt % was not suitable to be handled and therefore the furtherinvestigation was not carried out. On the other hand, the gel-coatedseed of the calcium chloride concentration of 20 wt % was appeared tohave sufficient strength to be handled in spite of its high hardness alittle and its recovered condition by absorbing water after drying wasappeared to be in a sufficient level, therefore its ratio of standing-upof seedling was investigated.

Example 2

[0052] An investigation was carried out using the same procedure as inComparative Example 2 except for points that the polymer B was employedinstead of the polymer A and that the calcium chloride concentrations of8, 10, 12, 14, 16 and 20 wt % were used. The gel-coated seeds (112 seedsper each solution) were prepared. (The water-containing hydrophilicpolymer grain dispersed in a gel-forming solution was observed with amicroscope revealing that the diameter of the grain was 0.1-0.2 mm andthe average diameter was 0.15 mm.)

[0053] The gel-coated seed of calcium chloride concentration of 8 wt %was not apparently suitable to be handled. Therefore, the othergel-coated seeds except it were subjected to the recovery by absorbingwater after drying. As a result, each recovered condition was appearedto be in a sufficient level, therefore each ratio of standing-up ofseedling was investigated.

Example 3

[0054] An investigation was carried out using the same procedure as inExample 2 except for a point that sodium alginate was weighed so thatits concentration in a solution became 0.5 wt % instead of 0.9 wt %. Thegel-coated seeds (112 seeds per each solution of the calcium chlorideconcentrations of 8, 10, 12, 14, 16 and 20 wt %) were prepared. (Thewater-containing hydrophilic polymer grain dispersed in a gel-formingsolution was observed with a microscope revealing that the diameter ofthe grain was 0.1-0.2 mm and the average diameter was 0.15 mm.)

[0055] The gel-coated seed of calcium chloride concentration of 8 wt %was not apparently suitable to be handled. Therefore, the othergel-coated seeds except it were subjected to the recovery by absorbingwater after drying. As a result, each recovered condition was appearedto be in a sufficient level, therefore each ratio of standing-up ofseedling was investigated.

Comparative Example 3

[0056] Further, gel-coated seeds were prepared in such a manner thatsodium alginate was weighed so that its concentration in a solutionbecame 0.5 wt %, and the concentration of the polymer A dispersed in thesolution became the same (0.8 wt %) as that of Comparative Example 2.

[0057] As a result, the gel-coated seed having sufficient hardness highenough to be handled was not obtained for each solution of the calciumchloride concentrations of 8-20 wt %. Consequently, the furtherinvestigation was not carried out as to these gel-coated seeds.

[0058] (Investigation on Ratio of Standing-up of Seedling)

[0059] The ratio of standing-up of seedling was investigated as to thegel-coated seed (gel-coated seed of a long onion), in which the grainsconsisting of the water-containing hydrophilic polymer are distributedin the coating gel-layer consisting of alginic acid-based aqueous gel.The result is shown in Table 1. TABLE 1 Concentration ConcentrationRatio of Hydro- of of hardening standing-up of philic sodium alginateliquid seedling Polymer (wt %) (wt %) (%) Comparative A 0.9 12 61.6Example 1 14 58.0 10 62.5 12 60.7 Example 1 B 09 14 61.6 16 58.9 20 54.510 63.4 12 63.4 Example 2 B 0.9 14 61.6 16 61.6 20 59.8 10 86.6 12 88.4Example 3 B 0.5 14 89.3 16 87.5 20 88.4

[0060] The examples and comparative examples described above reveal thatas for the gel-coated seed of the present invention, the coatinggel-layer can be completely recovered after the storage under dryingeven when the amount of the hydrophilic polymer is increased, and theratio of standing-up of seedling can be significantly improved byreducing the concentration of alginic acid. Moreover, the gel-coatedseed of the present invention is significantly advantageous incontrolling the production of the gel-coated seed because the tolerancerange of the concentration of the hardening liquid can be broad, whereasa very strict control of the concentration has been neededconventionally. Furthermore, the gel-coated seed of the presentinvention can be precisely sown by mechanical sowing.

[0061] The aforementioned preferred embodiments are described to aid inunderstanding the present invention and variations may be made by oneskilled in the art without departing from the spirit and scope of thepresent invention.

What is claimed is:
 1. A gel-coated seed comprising: a seed of a plant;a coating gel-layer, which coats the seed, consisting of alginicacid-based aqueous gel gelled in the presence of a multivalent metalion; and grains consisting of water-containing hydrophilic polymer,which is resistant to the multivalent metal ion, distributed in thecoating gel-layer.
 2. The gel-coated seed according to claim 1, whereinthe hydrophilic polymer is a carboxymethylcellulose-based hydrophilicpolymer.
 3. The gel-coated seed according to claim 1 or 2, wherein themultivalent metal ion is a calcium ion.